This invention relates to a method and apparatus for growing biomass particles, particularly microcarrierbound cells. More particularly, this invention relates to an improved particle settling chamber which is used in conjunction with an agitated suspension culture vessel, also known as a perfusion culture bioreactor.
In recent years there has been rapid growth in the development of various methods for the culturing of cells in suspension with the goal of attaining high cell densities. Batch culture systems, which utilized a fixed amount of nutrient medium, have been replaced with continuous or semi-continuous basis as described, for example in U.S. Pat. No. 4,166,768. In such continuous systems spent culture medium is withdrawn through a filter, which is immersed in the agitated culture medium. This filter is inevitably subject to clogging, which limits the time the continuous system can be operated.
In U.S. Pat. No. 4,335,215, there is disclosed a modified continuous culture system which is said to improve the growth of microcarrier-bound cells. In this modified system, the immersed filter of the prior systems is replaced with a settling chamber which is external to the main culture vessel. During operation, culture medium is withdrawn from the main agitated culture vessel through a narrow tube into the bottom of the settling chamber then out through the top of the chamber, since there is no agitation in the settling chamber, the microcarrier beads slowly settle by gravity to the bottom of the settling chamber and back through the narrow tube into the main agitated culture vessel, when the microcarrier beads contact each other along the sloping surfaces of the settling chamber and in the narrow tube, this is said to promote aggregation of beads and bead-to-bead cell growth.
There are several problems associated with the above-described systems. The bottom opening of the settling chamber and the narrow tube which connects the settling chamber to the main vessel have a relatively small diameter. The diameter of the connecting tube is generally dictated by the size of the port available on the main vessel. In these narrow areas the upward fluid velocity of medium is often significantly higher than the settling velocity of the beads, causing the beads to become clogged. In fact, this problem is partially addressed by the patentee who suggests reversal of the pumps to ensure free movement of the beads in the narrower portions.
Another problem associated with this design concerns sterilization of the system. Since the settling chamber is external to the main reactor, the chamber and all connections are difficult to sterilize and to maintain sterility during operation.
Citation of documents herein is not intended as an admission that any of the documents cited herein is pertinent prior art, or an admission that the cited documents is considered material to the patentability of any of the claims of the present application. All statements as to the date or representation as to the contents of these documents is based on the information available to the applicant and does not constitute any admission as to the correctness of the dates or contents of these documents.